Pumps for pumping molten metal are used in furnaces in the production of metal articles. Common functions of pumps are circulation of molten metal in the furnace or transfer of molten metal to a remote location along risers that extend from a base of the pump connected to conduit that extends to the remote location. The transfer function of the pump avoids a tapping operation which is dangerous and problematic. The pump may be located in a separate, smaller chamber such as a pump well adjacent the main hearth.
Currently, many metal die casting facilities employ a hearth containing a large proportion of the molten metal volume of the furnace. Solid ingots of metal may be periodically melted in the hearth. Metal scrap such as from aluminum cans is often charged into the molten metal in a scrap well adjacent the hearth. A transfer pump may be located in a separate well adjacent the hearth. The transfer pump draws molten metal from the well in which it resides and transfers it into a ladle, for example, from which the molten metal is taken to a holding furnace and fed into a plurality of die casters that form metal articles. Die casting furnaces often employ only a transfer pump, not a circulation pump. When scrap metal is added, it lowers the temperature of the molten metal. Burners located above the molten metal in the hearth must maintain molten metal temperature while compensating for the drop in temperature caused by scrap charging. A tremendous amount of fuel is required by the burners to heat and maintain the molten metal at a suitable temperature. In view of the heat applied by the burners at the surface of the molten metal and the cold scrap added to the bath, temperature differences arise in the bath.
Significant considerations in a die casting facility include the consumption of fuel and cleanliness and physical properties of the cast metal articles. Aluminum oxide is formed on the surface of the molten metal as the molten aluminum oxidizes. Aluminum oxide has an affinity for hydrogen gas. It is undesirable to have hydrogen gas in the metal. As the cast metal solidifies it releases trapped hydrogen gas, forming pin holes in the metal articles. Higher temperatures of molten aluminum lead to increased absorption of hydrogen gas and increased pin hole defects with resulting compromise in the physical properties of the metal articles.
An apparatus made by High Temperature Systems Inc. moves molten metal using a pump into a CORIOLIS® scrap charging vessel as described in U.S. Pat. No. 7,497,988 (“CORIOLIS® vessel patent”), which is incorporate herein by reference in its entirety. The pump can include a riser and a conduit that extends through a separating wall between a pump well and a charging well. Or, there may be no wall between the pump and scrap charging vessel. The molten metal that passes through the scrap charging, vortexer vessel leaves it through a lower passage in the vessel, thereby entering the well. The metal can be pumped through a lower archway of the separating wall between wells and through the higher opening in the separating wall into the scrap charging vessel. Another approach is to physically remove the refractory separating wall between wells. Metal processing companies have expressed a reluctance in removing the separating wall because it is very labor intensive and costly to do so.
A suitable pump made by High Temperature Systems, Inc. for use with the CORIOLIS® scrap charging vessel is a CHAMELEON® multifunctional pump as described in U.S. Pat. Nos. 7,687,017 and 7,507,365 (“the CHAMELEON® pump patents”), which are incorporated herein by reference in their entireties. The pump is designed to move an impeller into one, two or three stacked impeller chambers extending along the same vertical axis. This enables the pump to discharge the molten metal for circulating the molten metal of the furnace and to transfer the molten metal to one or more locations depending on which impeller chamber the impeller is positioned for rotation. For example, the molten metal can be sent through a conduit extending through the separating wall into the scrap charging vortexer vessel when it is desired to add scrap to the molten metal. On the other hand, during other periods when scrap is not charged, the molten metal can be circulated through the furnace, which reduces the effects of temperature gradients. This circulation can occur through a lower through-passageway in the scrap charging vessel.